A technique for highly selective and sensitive analysis of drugs using fluoroimmunoassay will be developed. The technique will be homogeneous, requiring no separation of bound from free labelled-antigen. Instead, the free labelled-antigen will be distinguished from the antibody-bound labelled-antigen on the basis of the difference in fluorescence lifetimes of the fluorescent label in the two different environments. Phase-resolved fluorescence spectroscopy, in which the fluorescence intensity of a species is nulled based on its fluorescence lifetime, will be used to measure the percents of free and antibody-bound labelled-antigen in the test solution. Calibration curves will constructed using standard solutions of non-labelled antigen. The problem of background fluorescence in serum and other biological samples will be minimized by the use of synchronous excitation in conjunction with phaseresolved fluorimetry. The technique will be developed for the analysis of two drugs, phenobarbital and primidone. Future work will then involve the production of suitable antibodies for determination of controlled substances such as methaqualone, phencyclidine, heroin, and other abused drugs. The technique will be applicable to clinical, toxicological, and forensic drug analysis.